Trash/Refuse Incineration/Recycling
Unlock all answers in this set
Unlock answersquestion
Middens
answer
- An old dump for domestic waste. -Used middens for all of our biodegradable waste like shells, animal bone, excretement etc. -Didn't work in cities.
question
Burning Dumps
answer
-First established in the 18th century in cities to control waste. -Early ones burned mostly natural materials. -Most of our trash now ends up in landfills, only some goes to municipal trash burning area.
question
Solid Waste Management Hierarchy
answer
-Reduce -Reuse -Recycle and compost -incineration with energy recovery -Landfill -Disagreement over how to rank the last two.
question
Which two countries lead in producing the most trash?
answer
-Ireland and then the U.S.
question
Solid Waste
answer
-Any material that is discarded, whether it is recycled, stored, or destroyed -Excludes municipal wastewater, industrial wastewater, nuclear waste, and some special wastes. -Municipal solid waste -Industrial -Special (Subset of infectious waste (physicians, dentists, veterinarian etc.) -Hazardous (toxic, waste that is highly acidic/ basic, unstable materials that have the potential to explode)
question
Municipal Solid Waste
answer
-MSW consists primarily of household waste, but includes waste from commercial activities and some industrial waste. -Composition is mostly paper and paperboard, then yard trimmings, food scraps, plastics...
question
Sanitary Landfill Layers
answer
-Clay barrier prevents soil and water contamination. Elongated shape elongates even more when compacted. -Plastic Liner prevents soil and water contamination. -Leachate collection= perforated pipes in a layer of sand collect rainwater that has filtered through the landfill (leachate). -Refuse cell= compacted garbage surrounded by soil from daily cover. 1 cell= 1 day's trash. -Daily cover prevents interactions between the air and the waste, prevents aerobic phase when the waste begins to decompose from interacting with the air. Comprised of soil.
question
Sanitary Landfill
answer
-Have a plastic liner which captures leachate -Methane is a product of landfills -Use daily cover of soil
question
Life Cycle of a Landfill
answer
-Aerobic Phase - during active landfilling and prior to daily cover there is enough oxygen entrapped in the waste to allow aerobic decomposition of wastes -Acid Phase - after oxygen is used up in aerobic decomposition, anaerobic processes take over. -Unsteady Methanogenesis Phase - Another group of bacteria, called methanogens, convert the organic acids into methane and carbon dioxide. The pH rises slightly in this phase and there is less leaching of metals. -Steady Methanogenesis Phase - As moisture and nutrients decline in each cell, methanogenesis slows down. During this phase, methane and carbon dioxide are the primary fermentation products. This phase can last for years, and possibly decades, until methane production stops.
question
Acid Phase of Landfill
answer
-Fermentation reactions break down cellulose and starch into simpler products that are fermented into hydrogen ions, CO2, fatty acids and alochols -Later, bacteria called acetogens further ferment the fatty acids into simpler organic acids including acetic acid and butyric acid (component of landfill smell) -As these acids form, the pH drops and metals can be leached from the waste. -The CO2 level rises and small amounts of hydrogen ions are produced.
question
Landfill failure
answer
-Subsidence from inadequate compaction -Formation of voids when putrefiable material ferments and produces liquid -Movement of water through landfill. -Contamination of groundwater and surface water (leachate) -Leachate
question
Leachate
answer
-The liquid that leaks from the landfill. -Formed from fermentation, dissolved iron, and low pH.
question
Incinerator Pro
answer
-Reduces trash volume from 75% to 90% -Residual ash is less toxic and mobile than waste in landfill. -Ash monofills are much more stable than MSW landfills and do not generate leachate and therefore do not contaminate GW. -Infectious waste is destroyed in incinerators. -Most organic compounds are destroyed in seconds whereas in landfills -Heat generated can be recovered as boiling water to use steam to turn turbines for electricity. -Air pollution control can be done at point source rather than over a large area.
question
Incinerator Con
answer
-Toxics are converted into gases and vapors that must be controlled; control is more difficult in the vapor phase b/c these compounds become more mobile. -Particulates including metals and toxic organic compounds are released and must be controlled. -Fly ash and bottom ash contain metals and other toxins that must be stabalized. -Toxic Secondary pollutants can form in gas phase -Dioxins
question
Dioxins
answer
-Chlorinated organic compounds produced when complete carbon is heated to high temperatures in an envt. that includes chlorine. -They bioaccumulate and are linked to reproductive and endocrine dysfunction in animals -Secondary pollutants that form in the gas phase -Biomagnify in the food chain -Present in dustballs -Present in animal products
question
Mass Burn
answer
-Most incinerators use Mass Burn technologies -Minimal sorting at the front end (curb) -All sorting is done at the \"pit\" and only very large unburnable objects are removed -Energy recovery is compromised by uneven \"fuel\"
question
Refuse-Derived Fuel
answer
-Requires better sorting at the front end (curb) -Additional sorting at the facility prior to incineration -Fuel is processed into uniform cubes -Energy recovery is more efficient than with Mass Burn
question
Water Wall Incinerator
answer
-Water wall furnace - heat is transferred through steel tubes filled with circulating water that line the walls of the furnace. -Most common MSW incinerator. -Efficient energy transfer.
question
Refractory Furnace
answer
-Heat transferred to a waste heat boiler through circulating air. -Older design -Less efficient heat transfer -Like a big oven.
question
Rotary Kiln
answer
-Rotating furnace lined with refractory brick -Small, with lower \"throughput\" rate -Most common for medical (red bag) or hazardous waste -Not often used for MSW -Better control of gas phase reactions than conventional furnaces.
question
Mass Burn Process
answer
-Waste is dumped on the tipping floor and then moved into the \"pit\" -Clamshell loads waste onto moving grate (or, in some incinerators, a ram feeds the waste) -Waste is burned in the primary combustion chamber at around 800C (1500F) -Heat is transferred to water or air and produces steam -Steam turns turbine and generates electricity -Solids fall through grate and are collected as bottom ash -Gas phase contaminants and particulates flow to the secondary combustion chamber -The gas phase contaminants are heated to approximately 900C (1800F) for at least two seconds to break down gas molecules and control gas phase reactions -Gas phase then is released as flue gas and goes to Air Pollution Control System -Solids in the flue gas are collected on filters or using electrostatic precipitators as fly ash
question
Fly Ash
answer
-Comprised of fine particulates -Fly ash rises with flue gases and enters the atmosphere
question
Bottom Ash
answer
-non-combustible material left over from incineration.
question
Refuse Derived Fuel
answer
-Processes are similar to those for Mass Burn after front end processing -More efficient energy recovery because non-combustibles and low heating value components are removed -Fuel is pelletized and has more surface area; also even combustion -Fewer metals in both bottom ash and fly ash -Flue gas is cleaner, but acid gases and dioxins are still of concern. -RDF can be adapted for single stream wastes, such as Tire-Derived Fuel.
question
Ash Monofill
answer
-A monofill is a landfill that contains only one type of waste -Ash monofills contain only ash -Normally, fly ash and bottom ash are mixed -Often, a stabilizer, such as cement, is added to prevent leaching of metals from ash -Ash monofills can be compacted better than MSW landfills, and are less subject to subsidence and leaching -Because incineration reduces MSW volume 75-90 %, ash monofills have a longer lifespan than MSW landfills.
question
Ash Recycling
answer
-Bottom ash can be used as a substitute for aggregate in concrete and asphalt mixtures -The primary barriers to doing this now are metals in the ash and cost -Fly ash can be used as a replacement or extender for Portland cement in concrete mixtures -It also has uses as a soil stabilizer, as a binder in asphalt mixtures, and in making bricks -Fly ash has engineering properties similar to those of clay, and also has properties similar to those of cements -The primary barriers right now are cost and metals present in the fly ash
question
Fly Ash Bricks
answer
-one way to recycle fly ash -Lighter than clay brick -More water resistant than clay brick -Concerns with leaching of toxic metals
question
Recyclable Materials
answer
-Many materials can be recycled, but the cost of processing them can be a barrier to an effective program -The materials with the highest economic values are metals, paper, cardboard, glass, and plastics -Products that have multiple components are more difficult and less cost-effective for recycling
question
Approaches to Recycling
answer
-Source separation= requires households to do some basic level of material sorting. Most common-separate paper from other materials. Alternative multiple sorts, paper, plastic, metals. -Single Stream- all recyclable materials go into the same container. Requires development of infrastructure to handle sorting whilst as the processing facility.
question
Metals
answer
-Ferrous metals= contain iron and is magnetic. Steel is the most commonly recycled ferrous metal. -Nonferrous metals= does not contain iron and not magnetic. Aluminum is the most commonly recycled nonferrous metal (most cans are nonferrous b/c they are lighter and it costs less to transport.
question
Ferrous Metals
answer
-6% of MSW -Major component - steel can, commonly called a \"tin\" can -Steel cans are coated with a thin coating of tin that has to be removed by heating A-pproximately 12 million tons/year of steel waste is present in MSW; only about 15 percent of this is recycled -Most recycled steel comes from outside the MSW stream - structural steel
question
Nonferrous Metal
answer
-Aluminum is the principal nonferrous metal in the MSW stream -Aluminum constitutes <2 percent of MSW by weight, but it is the most economically viable material for recycling -Approximately 3 million tons are generated in MSW each year; about half is recycled -Recycling 40 aluminum cans saves the energy equivalent of 1 gallon of gasoline -Most aluminum cans used in the US and Canada are made from recycled cans.
question
Cardboard
answer
-Single largest component of MSW by weight. -Two kinds- flat and corrugated. -Corrugated= Mostly boxes from packaging and shipping -Flat= Includes thin paperboard (Cereal boxes, shoe boxes, tissue boxes, etc.) -Approximately 80 percent of consumer products are packaged in cardboard (and most of the rest are in plastic!) -One ton of cardboard takes up approximately 9 cubic yards of landfill space -Approximately 70 percent of cardboard is currently recycled, most of it by businesses.
question
Glass
answer
-Mixxed glass=Most common in MSW stream Clear, amber, green, blue... -Clear glass= Has highest economic value -Approximately 7 percent of MSW by weight; about 20 percent is recycled -Crushed glass (cullet) can be re-melted into glass, but cullet from mixed glass is usually not recycled and is used as landfill cover.
question
Glass Recycling
answer
-Sort by color. -Crushed (cullet). -Mixed with limestone, silica sand, and soda ash. -Melted at high temperature. -Molten glass poured into molds. -Cooled, packed, and shipped.
question
Plastic
answer
-Approximately 7 percent of MSW by weight, but nearly half of MSW by volume -Difficult to recycle because of mixed plastic types in MSW -Most mixed waste is not separated and is \"one-cycled\" into plastic lumber or plastic lawn furniture
question
3 Categories of Paper Recycling
answer
-Mill broke= scraps and trimmings generated during production. It is recycled within the paper plant. -Pre-consumer waste= off-spec material that never reaches the consumer, never leaves the factory -Post-consumer waste= waste generated by consumers and recycled into manufactured goods.
question
Sorting (Paper recycling)
answer
-Highest quality paper comes from sorted paper types. -Quality in decreasing order:White paper/office paper, Magazines/glossies, Newsprint, Paperboard, Corrugated cardboard, Low quality paperboard -Waste paper can be used to make paper of equal or lower quality. -Mixed paper can be recycled up to 7 times before the fiber length is too short to produce paper. -The \"life\" of paper can be increased by adding some virgin fibers at each recycling round Paradoxically, paper made from 70-80 percent post-consumer waste is more sustainable than 100 percent post-consumer waste paper!
question
Pulping (Paper Recycling)
answer
-The pulper chops paper into smaller pieces The pieces are mixed with a screw device and water is added The pH is adjusted to 8.5-10.0 using sodium silicate or sodium hydroxide The screw mixes the pulp until it is a flowable slurry.
question
Cleaning and Screening (Paper Recycling)
answer
-A centrifuge is used to spin the pulp and materials that are denser than the pulp fibers move outward and can be removed -The pulp is then put through screens that remove objects larger than pulp fibers -Common contaminants include paper clips, staples, rubber erasers, other foreign material, and materials collectively called \"stickies\", which includes adhesives, laminates, and waxy material.
question
Deinking (Paper Recycling)
answer
-Deinking processes include froth floatation, wash deinking, and dissolved air floatation -The pulp is pumped into large tanks and the pH is maintained at 8.5-10.0 -Calcium is added, using either lime or calcium chloride -A fatty acid emulsion is added. -The goal of deinking is to dissolve the hydrophobic inks in the fatty acid and then to remove them either in a floating froth or by washing -In froth floatation or DAF, the fatty acid \"collector\", being less dense than water, floats in bubbles and can be skimmed off the top. -In wash deinking, the hydrophobic dispersants, which can be fatty acids or siloxane, are added to the slurry, which is agitated -The water is then removed using filter presses, and the inks will be removed with the dispersants in the water.
question
Problems with Paper Recycling
answer
-Some new inks are comprised of very small particles suspended in a hydrophobic carrier and they do not disperse well. These inks have to be removed using an acid bath after conventional deinking -Temperature control is critical during pulping and deinking in order to ensure a quality product.
question
Washing/ Dewatering (Paper Recycling)
answer
-If Froth Floatation was used, more water is added and the mixture is agitated -Filter presses are used to remove the water along with any remaining ink or stickies.
question
Dispersing (Paper Recycling)
answer
-Other chemicals, including chelating agents, are added to remove any remaining ink or other contaminants.
question
Bleaching (Paper Recycling)
answer
-If white paper is desired, the slurry must be bleached -Most recycled paper manufactures use peroxide or hydrosulfite bleaches and not chlorine or hypochlorite, which can increase the probability of producing dioxins in the wastewater.
question
Papermaking
answer
The reclaimed paper fibers are now made into paper using the same processes used to make virgin paper.
question
By-products of paper recycling
answer
-Sludge contains inks, stickies, plastic, short fibers, and other material. -There is some value to paper sludge as a fertilizer; what cannot be reused is buried in a landfill. -Some paper plants have retrofitted boilers to burn paper sludge to produce energy. -A plant near Rochester, NY is producing ethanol from paper sludge and other wastes.
question
Paper Construction Bricks
answer
-Sludge from paper manufacturing can be mixed with clay -Fired in kiln. -Used to produce bricks that can be used in construction.
